QINGDAO, China (Reuters) — U.S. Defense
Secretary Chuck Hagel visited China's sole aircraft carrier on Monday in
an unprecedented opening by normally secretive Beijing to a potent
symbol of its military buildup.

A U.S. official said the visit to the carrier the Liaoning, at a
port in the northern city of Qingdao, lasted about two hours. No
other details were immediately available.

The official believed Hagel was the first official visitor from
outside China to be allowed on board the Liaoning, although that
could not be immediately confirmed.

China's Defence Ministry confirmed the visit would happen but did
not provide details.

Chinese security experts said Beijing could be trying to quell U.S.
criticism that it was not transparent about its military
modernization.

Hagel's carrier visit, at the start of his three-day trip to China,
was quietly approved by Beijing at Washington's request, the U.S.
official said, speaking on condition of anonymity.

The 60,000-tonne Liaoning, a Soviet-era vessel bought from Ukraine
in 1998 and re-fitted in a Chinese shipyard, is seen as a symbol of
China's growing naval power and ambition for greater global
influence.

The carrier has yet to become fully operational, however, and
military experts say it could be decades before China catches up to
the far superior and larger U.S. carriers — if ever.

Hagel arrived in Qingdao after a trip to Japan.

Reporters travelling with Hagel did not accompany him on the vessel,
in what is a rare visit to a sensitive Chinese military site.

"It's a sign of openness, of sincerity, that China has nothing to
hide and wants to improve military relations with the United
States," said Ni Lexiong, a naval expert at the Shanghai University
of Political Science and Law.

"It will also be a good opportunity for the Americans to see the
difference between the Liaoning and their aircraft carriers," Ni
said, referring to the technological gulf between the two countries.

CHINA GETS REGULAR ACCESS

Chinese military brass are no strangers to U.S. warships, including
aircraft carriers.

Officers from the People's Liberation Army are routinely flown to
U.S. aircraft carriers en route to occasional port stops in Hong
Kong, according to U.S. military officials.

Their U.S. counterparts provide tours of the ship and flight deck
during operations — efforts U.S. diplomats say are geared to nudging
China towards greater transparency about its capabilities.

Ian Storey, a Singapore-based regional security expert, said earlier
that Hagel's visit would be "long on symbolism but short on actual
operational capabilities".

"By showing him a vessel that was built in Ukraine in the 1980s and
remains only a training platform that is still not fully
operational, the Chinese will be keeping him away from their more
sensitive capabilities, such as their missile programs or submarine
fleets," said Storey, of Singapore's Institute of South East Asian
Studies.

China is building submarines, surface ships and anti-ship ballistic
missiles, and has tested emerging technology aimed at destroying
missiles in mid-air.

The carrier visit came a day after Hagel said he would use his first
trip to China as defense secretary to press Beijing to use its
"great power" wisely and respect its neighbors, who have been put on
edge by the country's growing assertiveness in Asia's disputed
waters.

China claims 90 percent of the 3.5 million sq km (1.35 million sq
mile) South China Sea, which is believed to be rich in oil and gas.
The Philippines, Vietnam, Malaysia, Brunei and Taiwan all claim
parts of those waters.

China has a separate dispute with Japan in the East China Sea over
uninhabited islets that are administered by Japan. China's decision
in November to declare an air defence identification zone in the
area that includes those islands sparked protests from the United
States, Japan and South Korea.

China's official Xinhua news
agency, in a commentary released as Hagel arrived, said Hagel had to
show he was sincere about improving ties and the United States had
to "assure its China friend of its intentions".

"As the world's second- and first-largest economies, China and
America have a shared interest in a stable environment to facilitate
economic prosperity. Neither of them, nor the global economy, can
afford confrontation or conflict," Xinhua said.

RISKS OF A MISHAP

Hagel, in his talks in Japan over the weekend and last week at a
gathering of Southeast Asian defense chiefs in Hawaii, had sought to
reassure allies of the U.S. security commitment to the region and
has promised frank discussions in China.

China, in turn, has repeatedly urged the United States not to take
sides in any of its disputes in the region, and has watched warily
as Washington moves to strengthen its military alliances, especially
with Tokyo and Manila, as part of its strategic "pivot" toward Asia.

"Both sides are aware of the potential for military clashes, and the
need to increase understanding and manage and reduce the risks, so
this visit is a positive sign," said Zhu Feng, director of the
International Security Programme at Peking University.

The risks of a mishap were highlighted in December when the American
guided missile cruiser USS Cowpens had to take evasive action in the
South China Sea to avoid hitting a Chinese warship operating in
support of the Liaoning.

The Chinese carrier is the first step in what state media and some
military experts believe will be China's deployment of several
locally built carriers by 2020.

While President Xi Jinping recently urged China's military
leadership to work faster to get the carrier combat-ready, some
Chinese analysts and parts of the state media appear keen to dampen
expectations about the Liaoning, which went on its first training
mission into the South China Sea late last year.

The Liaoning would serve as a training platform rather than a
fighting weapon, some Chinese experts have said.

Considerable doubt also remains over when it will be fully
operational. Earlier estimates of two or three years had grown
rubbery, with some hints internally that it could stretch to a
decade, some experts say.

(Additional reporting by Ben Blanchard in Beijing and Greg Torode in
Hong Kong; editing by Dean Yates and Robert Birsel)